JP2024508757A - Accessory devices to improve wireless power transfer efficiency - Google Patents

Abstract

An accessory (300) for improving wireless transmission efficiency in a wireless transmission system reduces magnetic flux coupling from a transmitter winding (103) to friendly metal of a power receiver (104) and/or 103) to the receiver winding (105). The core can define an aperture that corresponds to an outer dimension (eg, outer diameter) of the receiver winding. The core further includes an outer surface selected to block sufficient magnetic flux to reduce flux coupling to the friendly metal of the receiver, such as an outer dimension that corresponds to the outer dimension (e.g., outer diameter) of the transmitter winding. may have dimensions. The accessory may be a case for the power receiver device (104) or may be configured to attach to the face of the power transmitter device (102) and may include one or more alignment fixtures. .

Description

An exemplary wireless (inductive) power transfer system is shown in FIG. The efficiency of wireless (inductive) power transmission between the wireless power transmitter (PTx) 102 and the wireless power receiver (Power Receiver, PRx) 104 is determined by the efficiency of the wireless (inductive) power transmission between the PTx (winding 103) and PRx (winding 105). It depends on the degree of magnetic coupling between the respective windings. The wireless (inductive) power transfer winding is preferably a coil wound from a suitable wire such as magnet wire or Litz wire, or on a printed circuit board (PCB) or flexible printed circuit board (flex circuit). It can take a variety of forms, including formed traces. These windings may be considered to be generally circular, and may be generally planar, but do not necessarily need to be planar. Generally circular means that the windings form a closed loop, but the shape can be any closed form, including square, rectangular, circular, oval, polygonal, and other shapes, including rounded It may have curved corners, but this is not always the case. Additionally, the windings often have a thickness that corresponds to the distance between the outermost turns of the winding and the innermost turns of the winding. For example, a circular winding may have an outer diameter (corresponding to the diameter of the outermost turn) and an inner diameter (corresponding to the diameter of the innermost turn of the winding). Depending on the context, "diameter" as used herein may refer to either the outer diameter, the inner diameter, or the average of the two. "Diameter" also refers to similar internal dimensions of windings that are not strictly circular in shape, such as the length of the sides of a square winding, or the length of the major or minor axis of a rectangular or elliptical winding. It can be understood as encompassing the outer dimensions.

One factor that can affect the degree of magnetic coupling between windings is the relative size of these windings. If there is a magnitude mismatch between the PTx and PRx coils, the magnetic flux from the PTx winding can couple to metal structures of the power receiving device other than the power receiver winding. Such structures are known or sometimes referred to as "friendly metals." This coupling may be undesirable because it wastes energy from the transmitter and causes a loss in efficiency. In some cases, such undesirable magnetic coupling may also lead to one or both of the PTx and PRx devices misinterpreting the amount of wireless power being transmitted, leading to feedback loop problems.

In a wireless power transfer system comprising a power transmitter (PTx) having a PTx winding and a power receiver (PRx) having a PRx winding, the PTx winding and the PRx winding are dimensionally mismatched. Accessories for improving efficiency can include a core formed from a material with selected magnetic properties. The core is dimensioned to perform at least one of: reducing flux coupling from the PTx windings to the PRx friendly metal; and enhancing flux coupling from the PTx windings to the PRx windings. and may be arranged. The core may be a ferrite core. The dimensional mismatch between the PTx and PRx windings can include the PTx winding being larger than the PRx winding. In such a case, the core may define an aperture that corresponds to the outer dimensions of the PRx winding. The core can have outer dimensions selected to block sufficient magnetic flux to reduce flux coupling of the PRx to friendly metal. The aperture can have an inner diameter that corresponds to the outer diameter of the PRx winding. Accessories may be configured in a variety of forms including shims configured to attach to either the PTx or PRx by adhesives, magnets, mechanical features, and the like. The accessory may be configured as a case for an electronic device such as a smartphone, smartwatch, etc.

The accessory is configured to improve wireless power transfer efficiency between the electronic device and the wireless charger when the wireless charging winding of the electronic device and the wireless charging winding of the wireless charger are dimensionally mismatched. can be done. The accessory can include a core formed from a material having selected magnetic properties, the core reducing magnetic flux coupling from the wireless charging winding of the wireless charger to the metal of the electronic device, and sized and arranged to perform at least one of: enhancing magnetic flux coupling from the wireless charging winding of the device to the wireless charging winding of the device. The accessory can further include one or more alignment fixtures. The one or more alignment fixtures can be configured to align or secure the accessory with respect to the electronic device. Additionally or alternatively, one or more alignment fixtures may be configured to align or secure the case relative to the wireless charger. The alignment fixture can include one or more magnets. One or more magnets can form a ring. The core may be a ferrite core. The dimensional mismatch may include the wireless charging winding of the wireless charger being larger than the wireless charging winding of the electronic device. In such a case, the core may define an aperture that corresponds to the outer dimensions of the wireless charging winding of the electronic device. The core can have outer dimensions selected to block sufficient magnetic flux to reduce magnetic flux coupling to friendly metals of the electronic device. The aperture can have an inner diameter that corresponds to an outer diameter of a wireless charging winding of the wireless charger.

The wireless charging accessory device is designed to reduce magnetic flux coupling from the wireless power transmitter winding of a wireless power transmitter to the friendly metal of the wireless power receiver, or from the wireless power transmitter winding to the dimensionally mismatched wireless power receive winding of the wireless power receiver. means for enhancing magnetic flux coupling to and reducing magnetic flux coupling from a wireless power transmission winding of a wireless power transmitter to a friendly metal of a wireless power receiver, or from a wireless power transmission winding to a wireless power reception of a wireless power receiver; and means for aligning the means for enhancing magnetic flux coupling to the windings with respect to at least one of the wireless power receiver or the wireless power transmitter. A means for reducing magnetic flux coupling from a wireless power transmitting winding of a wireless power transmitter to a friendly metal of a wireless power receiver, or for enhancing magnetic flux coupling from a wireless power transmitting winding to a wireless power receiving winding of a wireless power receiver. , can be a ferrite core. The dimensional mismatch between the wireless power transmitting winding and the wireless power receiving winding can include the wireless power transmitting winding being larger than the wireless power receiving winding, and the core having an aperture corresponding to the outer dimensions of the wireless power receiving winding. Define. The core can have dimensions selected to block sufficient magnetic flux to reduce magnetic flux coupling to friendly metal of the wireless power receiver.

The accessory may be configured to be attached to the face of the wireless power transmitter to improve wireless power transfer efficiency between the electronic device and the wireless power transmitter, and the accessory can be configured to attach to the face of the wireless power transmitter to improve wireless power transfer efficiency between the electronic device's wireless charging winding and the wireless power transmitter. The dimensions of the charging winding do not match. The accessory can include a core formed from a material having selected magnetic properties, the core being capable of reducing magnetic flux coupling from the wireless charging winding of the wireless power transmitter to the metal of the electronic device and sized and arranged to perform at least one of: enhancing magnetic flux coupling from the electrical machine's wireless charging winding to the electronic device's wireless charging winding. The accessory may be configured to be attached to a surface of the wireless power transmitter by adhesive or by other methods such as mechanical fasteners. The core can be a ferrite ring dimensioned to shield the metal of the electronic device from magnetic flux induced by at least one wireless charging winding of the wireless power transmitter. The ferrite ring includes one or more ferrite rings sized and dimensioned to be placed near the one or more wireless charging windings of the wireless power transmitter to provide the desired level of shielding or flux redirection. Can contain tabs. The core includes an additional ferrite bar sized and dimensioned to be placed near one or more wireless charging windings of the wireless power transmitter to provide the desired level of shielding or flux redirection. It can further include.

FIG. 1 is a diagram illustrating a wireless power transfer system. FIG. 2 illustrates a wireless power transfer system showing magnetic flux coupling in situations where the coils have different dimensions. FIG. 2 illustrates a wireless power transfer system showing magnetic flux coupling in situations where the coils have different dimensions. FIG. 2 illustrates a wireless power transfer system with accessories interposed between PTx and PRx to improve wireless power transfer efficiency. FIG. 2 illustrates a wireless power transfer system with accessories interposed between PTx and PRx to improve wireless power transfer efficiency. 3 illustrates respective embodiments of accessories that improve wireless power transfer efficiency. 3 illustrates respective embodiments of accessories that improve wireless power transfer efficiency. 3 illustrates respective embodiments of accessories that improve wireless power transfer efficiency. 3 illustrates respective embodiments of accessories that improve wireless power transfer efficiency. 3 illustrates respective embodiments of accessories that improve wireless power transfer efficiency. 3 illustrates respective embodiments of accessories that improve wireless power transfer efficiency. 3 illustrates respective embodiments of accessories that improve wireless power transfer efficiency. 3 illustrates respective embodiments of accessories that improve wireless power transfer efficiency. FIG. 3 illustrates an embodiment of a magnetic flux shielding/direction accessory incorporating a ferrite core. Figure 9 shows further details of the flux shielding/redirection accessory of Figure 8; FIG. 3 illustrates an accessory for improving wireless power transfer efficiency that includes a segmented ferrite core with a corresponding magnet ring.

In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the concepts disclosed. As part of this description, some of the drawings of this disclosure depict structures and devices in block diagram form for clarity. In the interest of clarity, not all features of an actual implementation are described in this specification. Moreover, the language used herein was chosen solely for purposes of readability and explanation, and not to limit or limit the disclosed subject matter. Rather, the appended claims are intended to such an end.

Various embodiments of the disclosed concepts are illustrated in the accompanying drawings, by way of example and not by way of limitation, and like reference numerals indicate like elements. For simplicity and clarity of illustration, reference numbers have been repeated, where appropriate, in different drawings to indicate corresponding and/or similar elements. In addition, numerous specific details are set forth to provide a thorough understanding of the implementations described herein. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the relevant features being described. References in this disclosure to "an," "one," or "another" embodiment are not necessarily to the same or different embodiments, but mean at least one. It is something. A given drawing may be used to illustrate multiple embodiments of the present disclosure or multiple species of the disclosure, and not all elements in a drawing may be required in a given embodiment or species. do not have. Reference numbers, when given in a given figure, refer to the same element throughout several figures, but are not repeated in all figures. The drawings are not to scale unless otherwise indicated and proportions of certain parts may be exaggerated to better illustrate details and features of the disclosure.

2A and 2B illustrate a wireless (inductive) power transfer configuration including a magnitude mismatch between PTx winding 103 and PRx winding 105. In the illustrated configuration, PTx winding 103 has a larger diameter than PRx winding 105. In other situations not shown, the opposite may be true. In the side view of FIG. 2B, magnetic flux lines 202 illustrate an exemplary magnetic flux path associated with driving the PTx winding 103 (shown in the top view of FIG. 2A) in a counterclockwise direction. As seen in FIG. 2B, some of the magnetic flux lines 202 pass through the PRx winding 105. This portion of the magnetic flux may be considered to effectively couple to the PRx device. However, some of the magnetic flux lines 202 do not pass through the PRx winding 105, but rather enter the metallic components of the PRx device 104 (i.e., the aforementioned "friendly metal"), indicated by the "X" markings in FIG. 2B. reach. To the extent that some of the magnetic flux from 103 interacts with the friendly metal rather than the PRx winding 105, the magnetic coupling between PTx and PRx is reduced. This is due in part to the different dimensions of the PTx and PRx windings 103 and 105, respectively.

One way to address this magnitude mismatch and improve the degree of magnetic coupling between PTx windings 103 and PRx windings 105 is to provide magnetic flux shielding and/or redirection between PTx and PRx. Accessories should be provided. FIG. 3A shows a side view of such an arrangement, and FIG. 3B shows a top view of such an arrangement. The magnetic flux shielding and/or redirecting accessory may include a core 300 made of ferrite or other ferromagnetic material with suitable magnetic properties, such as sintered ferrite or nanocrystalline sheets. The core 300 is configured to shield the friendly metal of the PRx 104 from the magnetic flux induced by the PTx winding 104 and/or to effectively redirect some or substantially all of that magnetic flux to the PRx winding 105. Can be dimensioned.

In the illustrated example having a relatively large PTx coil 103 and a relatively small PRx coil 105, the ferrite core 300 has an inner diameter (ID) that generally corresponds to the inner diameter of the PRx coil and an otherwise friendly metal. It may have a ring shape with an outer diameter (OD) large enough to block magnetic flux from the coupled PTx coil. Magnetic coupling between the windings 103 and 105 is improved by arranging such a core 300 coaxially between the windings, substantially parallel to each winding, and substantially overlapping each winding. The magnetic flux coupling to the friendly metal of PRx device 104 may be reduced.

A nearly similar solution can be applied to the opposite situation where the PRx coil is larger and the PTx coil winding is smaller. Also, as mentioned above, the shape of each winding and core does not have to be strictly circular, and the diameter described above can be the length of the inner side, the length of the major axis, the length of the minor axis, etc. It may also be of any closed or nearly closed shape. By "substantially closed" shape it is to be understood that the core may be composed of two or more segments of magnetic material with relatively small gaps (compared to the core size) between the segments. . Importantly, the core 300 is positioned and dimensioned to reduce undesirable flux coupling from the PTx winding 103 to the friendly metal of the PRx device 104 and/or enhance flux coupling to the PRx winding 105. That's what it means. Additionally, although the described embodiment features a generally planar coil and core 300, the same principles apply to non-planar windings and non-planar intermediate core 300. In such embodiments, the intermediate core 300 may be shaped, shaped, or shaped to reduce undesirable flux coupling to so-called "friendly metal" and/or to increase the amount of flux coupling into the PRx windings. should be placed and dimensioned.

In various other implementations, the core 300 dimensionally matches the shape of a PTx coil instead of a PRx coil. For example, when the phone is placed inside the case, the ferrite core 300 can be aligned with the power transmitting winding 103 of the charging pad 102 such that the outer diameter of the ferrite core/ring 300 is aligned with the diameter of the power transmitter winding 103. , the inner diameter of the ferrite core/ring 300 is sized such that a central opening in the structure 300 allows magnetic flux to flow into the receiving window 105 of the telephone 104 . That is, the inner diameter of ferrite core/ring 300 is larger than the inner diameter of power receiving winding 105 of telephone 104. In some cases, the inner diameter of ferrite core/ring 300 is larger than the inner diameter of power receiving winding 105 and smaller than the outer diameter.

In various implementations of PTx device 102 and PRx device 104, the intermediate device incorporating core 300 may take various forms. As an example, as shown in FIG. 4A (top view) and FIG. 4B (side view), the PTx 102 may be a charging mat, and the PRx 104 may be a mobile phone, smart watch, tablet PC, wireless earphone charging case, or other The intermediate device incorporating the ferrite core 300 may be an accessory 400 for an electronic device. The accessory 400 may be a cell phone case, a "shim" that can be placed between the PTx and PRx, or another intermediate device that incorporates the ferrite core 300. Ferrite core 300 may be provided within an accessory 400, which is designed and dimensioned to properly position core 300 relative to the PRx winding of the PRx device. For example, when the phone is placed inside the case, the inner diameter of the ferrite core/ring 300 aligns with the outer diameter of the receiver winding 105, and the annular shape of the ferrite core/ring 300 aligns the friendly metal of the phone 104 with the PTx of the charging pad 102. Ferrite core 300 may be suitably aligned with receiving winding 105 of telephone 104 to shield it from the magnetic flux induced by winding 103 .

As shown in FIGS. 5A-5B, 6A-6B, and 7A-7B, cases 500, 600, or 700 each assist the user in aligning the accessory/phone combination with an external charging device. It may also optionally include one or more mechanisms for doing so. As an example, such an accessory, whether a case, shim, or otherwise, may be used to connect the accessory/device combination to a wireless power transmitter and/or a wireless power transmitter with complementary configured magnets. Alternatively, it may include one or more magnets that can serve to align the receiver device. This alignment can help align the respective coils of the device as well as align the ferrite core 300 with the PTx winding 103 and/or the PRx winding 105. In FIGS. 5A and 5B, magnet ring 502 is shown as being below ferrite ring 300, or in other words, ferrite ring 300 is placed between the magnet and a device (e.g., a phone, not shown). It is provided. Similar to the embodiment of FIGS. 4A and 4B, the ferrite ring 300 prevents magnetic flux from the power transmitter from coupling to the "friendly metal" of the device, reducing undesirable power losses and associated heat generation. Additionally, the magnets of magnet ring 502 may be segmented to reduce losses. In this embodiment, the accessory may be mechanically placed and secured to the device (according to various known techniques) and the magnet connects the device/accessory combination to a power transmitting device (e.g., a charging pad, not shown). ) may be used to assist in attachment and alignment. Additionally, as discussed above and in more detail below, the ferrite ring 300 may also be segmented, in which case the magnet ring segments and the ferrite ring segments are defined below with respect to FIG. May be interspersed as shown.

In FIGS. 6A and 6B, magnet ring 502 is shown as being above ferrite ring 300, or in other words, ferrite ring 300 is connected to a magnet and a power transmission device (e.g., a charging pad, not shown). is provided in between. Similar to the embodiments of FIGS. 4A-4B and 5A-5B, the ferrite ring 300 prevents magnetic flux from the power transmitter from coupling into the "friendly metal" of the device, resulting in undesirable power losses and associated Reduces heat generation. Additionally, the magnets of magnet ring 502 may be segmented to reduce losses. In this embodiment, the accessory (e.g., case or shim) may be magnetically secured (and aligned) to the device (e.g., phone), and the device/accessory combination charging pad). As mentioned above and as explained in more detail below, ferrite ring 300 may also be segmented, in which case the magnet ring segments and ferrite ring segments are arranged as shown below with respect to FIG. May be scattered.

7A and 7B, magnet ring 502 is shown as being generally in the same plane as ferrite ring 300. In FIGS. Strict coplanarity is not required and may not be possible depending on the respective heights of the magnet and ferrite core in a given embodiment. Similar to the embodiments of FIGS. 4A-4B, 5A-5B, 6A-6B, and 7A-7B described above, the ferrite ring 300 allows the magnetic flux from the power transmitter to be transferred to the "friendly metal" of the device. to reduce undesirable power losses and associated heat generation. Additionally, the magnets of magnet ring 502 may be segmented to reduce losses. In this embodiment, magnets may be used to securely position the accessory relative to both the device and/or the power transmission device (eg, charging pad).

In FIG. 10, as in FIGS. 7A and 7B, magnet ring 502 is shown as being substantially in the same plane as ferrite ring 300. In FIG. As mentioned above, exact coplanarity is not required, especially considering that the respective heights of the magnet and ferrite core may be different for a given embodiment. However, for packaging purposes, the magnet components in ring 502 and the ferrite components in ring 300 are made so that at least some of these components are coplanar so that the z-height of the resulting accessory is low. It may be useful to configure as above. Similar to the embodiments of FIGS. 4A-4B, 5A-5B, 6A-6B, and 7A-7B described above, the ferrite ring 300 allows the magnetic flux from the power transmitter to be transferred to the "friendly metal" of the device. to reduce undesirable power losses and associated heat generation. Additionally, the magnets of magnet ring 502 are segmented into segments "M" to reduce losses and improve manufacturability. Similarly, ferrite ring 300 is segmented into segments "F" interposed between magnet segments "M". As mentioned above, magnets may be used to secure and position accessories relative to the device and/or power transmission device (eg, charging pad). The relative sizes of the magnet segments and the ferrite segments may increase the distance between the accessory 1000 and the device (e.g., phone) and/or power transmitter (by increasing the size of the magnet), both radially and circumferentially. It may be adjusted as necessary to provide the required sufficient locking force and/or to increase the flux shielding/coupling effect (by increasing the size of the ferrite segments). In some embodiments, the relative placement of the magnet ring segments and ferrite ring segments may be such that the various segments are substantially collinear along the circumference of their respective rings. Depending on the specific dimensions of the ferrite ring segments and magnet ring segments, precise collinearity may not be required or provided, as wide collinearity around the circumference may be appropriate for some applications. .

FIG. 8 shows an alternative embodiment of a flux shielding/redirection accessory 801 that incorporates a ferrite core 300. The accessory 801 may be a shim device suitable for being placed on and optionally secured to the PTx device 102 itself. (As mentioned above, PTx device 102 may be, for example, a charging mat, a charging pad, or other suitable wireless/inductive charging device.) Accessory 801 also connects intermediate device 801 to PTx 102 and associated PTx Mechanical, adhesive, and/or magnetic features 802 may be included to align and/or secure windings 103. As mentioned above, the core 300 preferably reduces undesirable magnetic flux coupling to friendly metal of a PRx device (such as a mobile phone or other electronic device or accessory) and/or the PRx winding 105 of the PRx device. should be sized and arranged to enhance magnetic flux coupling to the Therefore, it needs to be positioned relative to the PTx winding 105 so as to interrupt and/or redirect the magnetic flux that would normally couple to the friendly metal of the PRx device.

FIG. 9 shows further details of embodiments 902, 904 of flux shielding/redirection accessory 801 (FIG. 8). In embodiments 902 and 904, PTx device 102 can include multiple transmission coils 103 configured as DDQ coils. Accessories 902, 904 may be placed between PTx device 102 and PRx device 104 (eg, a mobile phone). Accessories 902, 904 may include a ferrite ring 300 that may be implemented as a ferrite frame 300 surrounding the top/Q coil 103 of the PTx device 102. As a result, the friendly metal of PRx device 104 is effectively shielded from the magnetic flux induced by coil 103. Similarly, accessory 904 may include a ferrite frame that covers all or substantially all of the transmission area of PTx device 904. In such embodiments, additional ferrite bars 910 may be provided near particular coils as needed to provide the required level of shielding/flux redirection. Optional tabs 912 within ferrite ring/frame 300 may also be used to achieve a similar effect.

The above describes example embodiments of accessories for wireless power transfer systems that provide improved coupling between wireless power transmitter (PTx) and wireless power receiver (PRx) devices. Such systems may be used in a variety of applications, but when used with wireless charging devices (e.g., charging mats, charging pads, charging stands, etc.) that are configured for use with different devices. , is particularly advantageous when used with electronic devices such as mobile computing devices (e.g., laptop computers, tablet computers, smartphones, etc.) and their accessories (e.g., wireless earphones, styluses and other input devices, etc.). obtain. Although a number of specific features and various embodiments have been described, unless expressly stated to be mutually exclusive, various features and embodiments may be combined in various permutations in a particular implementation. I hope you understand what you get. Accordingly, the various embodiments described above are provided by way of example only and should not be construed as limiting the scope of this disclosure. Various modifications and changes may be made to the principles and embodiments herein without departing from the scope of the disclosure or the scope of the claims.

The techniques presented and claimed herein are referenced and applied to material objects and actual examples of a practical nature, which demonstrably improve the field of the art; not physical, intangible, or purely theoretical. Further, any claim in the claims appended at the end of this specification may include "means for [performing] ... [function]" or "means for [performing] ... [function]" or "means for [performing] ... [function]". 112(f), such elements are intended to be construed under 35 U.S.C. 112(f). However, for claims containing elements set out otherwise, it is intended that such elements not be construed under 35 U.S.C. 112(f).

Claims (22)

In a wireless power transmission system comprising a power transmitter (PTx) having a PTx winding and a power receiver (PRx) having a PRx winding, the PTx winding and the PRx winding are dimensionally mismatched. An accessory for improving power transmission efficiency, the accessory comprising:
a core formed from a material having selected magnetic properties;
reducing magnetic flux coupling from the PTx winding to the PRx friendly metal;
enhancing magnetic flux coupling from the PTx winding to the PRx winding;
an accessory dimensioned and arranged to perform at least one of the following: The accessory of claim 1, wherein the core is a ferrite core. the dimensional mismatch between the PTx winding and the PRx winding includes a PTx winding that is larger than the PRx winding, and the core defines an aperture that corresponds to an outer dimension of the PRx winding. , the accessory according to claim 1. 4. The accessory of claim 3, wherein the core has outer dimensions selected to block sufficient magnetic flux to reduce flux coupling of the PRx to the friendly metal. 5. The accessory of claim 4, wherein the aperture has an inner diameter that corresponds to an outer diameter of the PRx winding. An accessory configured to improve wireless power transfer efficiency between an electronic device and a wireless charger, wherein a wireless charging winding of the device and a wireless charging winding of the wireless charger are dimensionally mismatched. and the accessory is
a core formed from a material having selected magnetic properties;
reducing magnetic flux coupling from the wireless charging winding of the charger to metal of the device;
enhancing magnetic flux coupling from the wireless charging winding of the charger to the wireless charging winding of the phone;
an accessory dimensioned and arranged to perform at least one of the following: 7. The accessory of claim 6, further comprising one or more alignment fixtures. 8. The accessory of claim 7, wherein the one or more alignment fixtures are configured to align or secure the accessory with respect to the electronic device. 8. The accessory of claim 7, wherein the one or more alignment fixtures are configured to align or secure the accessory with respect to the wireless charger. 8. The accessory of claim 7, wherein the one or more alignment fixtures are configured to align or secure the accessory with respect to both the device and the wireless charger. 8. The accessory of claim 7, wherein the alignment fixture includes one or more magnets. 12. The accessory of claim 11, wherein the one or more magnets form a ring. The accessory of claim 6, wherein the core is a ferrite core. The dimensional mismatch includes the wireless charging winding of the wireless charger being larger than the wireless charging winding of the electronic device, and the core having an outer dimension of the wireless charging winding of the electronic device. 7. The accessory of claim 6, defining a corresponding aperture. 15. The accessory of claim 14, wherein the core has outer dimensions selected to block sufficient magnetic flux to reduce magnetic flux coupling to the friendly metal of the electronic device. 16. The accessory of claim 15, wherein the aperture has an inner diameter that corresponds to an outer diameter of the wireless charging winding of the wireless charger. 7. The accessory of claim 6, wherein the accessory is a case for the electronic device. 7. The accessory of claim 6, wherein the accessory is a shim configured to be placed between the device and the wireless charger. An accessory configured to be attached to a surface of the wireless power transmitter to improve wireless power transfer efficiency between the electronic device and the wireless power transmitter, the accessory comprising a wireless charging winding of the electronic device and the wireless power transmitter. There is a dimensional mismatch between the power transmitter's wireless charging winding and the accessory.
A core formed from a material having selected magnetic properties, the core comprising:
reducing magnetic flux coupling from the wireless charging winding of the wireless power transmitter to metal of the electronic device;
enhancing magnetic flux coupling from the wireless charging winding of the wireless power transmitter to the wireless charging winding of the electronic device;
a core dimensioned and arranged to perform at least one of the following:
an adhesive configured to secure the accessory to the surface of the wireless power transmitter;
and accessories. 20. The accessory of claim 19, wherein the core is a ferrite ring dimensioned to shield the metal of the electronic device from magnetic flux induced by at least one wireless charging winding of the wireless power transmitter. . one or more tabs sized and dimensioned such that the ferrite ring is positioned proximate one or more wireless charging windings of the wireless power transmitter to provide a desired level of shielding or flux redirection; 21. The accessory of claim 20, comprising: the ferrite core includes an additional ferrite bar sized and dimensioned such that the ferrite core is positioned near one or more wireless charging windings of the wireless power transmitter to provide a desired level of shielding or flux redirection; 21. The accessory of claim 20, further comprising: